In a system with rapidly rotating or moving parts, a flow of a fluid surrounding such parts may exhibit fluctuations (in pressure and/or velocity) or form turbulent patterns that exert undesirable fluid dynamic forces on components of the system. As one example, in data storage systems such as disc drives, the positioning of a read/write head relative to a track that is being accessed and/or its distance from the disc surface (commonly referred to as fly height) are subject to mechanical and vibrational disturbances due to a variety of sources, including fluid turbulence, resonant vibration modes, physical imperfections of the mechanical components, and external shocks, for example. The performance of a data storage system depends on the precision with which the read/write head is positioned proximate to target data tracks. The various mechanical and vibrational disturbances to which the head becomes subjected tend to counteract that precision, potentially causing “runout” errors in the signals intended to be read from the target data tracks. Some of those runout errors may be repeatable, manifesting as a superfluous periodic signal component such as those due to flaws in a rotating disc on which the data tracks are written. Other runout errors may be irregular and non-repeatable, such as those due to external shock, or to the fluctuations and/or turbulence of flow that may be generated by a rotating disc and adjacent components. Flow impinges upon the actuator arms and head gimbal assemblies (HGAs) that position read/write heads over the discs. The flow excites various mechanical vibration modes of the arms, HGAs, and discs that cause read/write head fly height fluctuations and off-track motion, which results in non-repeatable runout errors. In particular, arm/HGA sway modes, torsion modes, and bending modes are typically excited. As areal densities of disc drives increase, and the speed of rotation of the discs increases, the problems with non-repeatable runout due to flow excitation become a more severe performance constraint. This is representative of a variety of systems in which controlling fluid flow is becoming one of the primary obstacles in the path of continued advances in performance.
Systems, devices and methods are needed to control fluid flow, in order to reduce off-track vibrations and fly height fluctuations in disc drives with higher areal densities and higher disc speeds. Embodiments of the present invention provide solutions to these and other problems, and offer additional advantages over the prior art.